Buffered silane emulsions having low volatile organic compounds when cured

ABSTRACT

There are provided aqueous emulsions useful for rendering porous substrates water repellent having low volatile organic compound content when cured comprising effective amounts of (a) a hydrolyzable silane having a determinable pH-stable range, (b) an emulsifying agent having an HLB value of from 2 to 20, (c) a buffering compound to maintain the composition within the pH-stable range; and (d) water. Such buffered compositions are stable on long term storage and maintain high effective levels of active silane content even when they include biocides which may accelerate the hydrolysis of aqueous silane-containing compositions.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of commonly assignedco-pending application, Ser. No. 189,146, filed May 2, 1988, now U.S.Pat. No. 4,877,654.

FIELD OF THE INVENTION

This invention relates to buffered aqueous systems which are especiallyuseful for rendering porous substrates water repellent. Moreparticularly, the present invention relates to buffered emulsions ofaqueous silanes, and/or oligomers thereof which have low levels ofvolatile organic compounds (VOC) when cured, and are useful in treatingporous masonry and wood surfaces to render such surfaces waterrepellent, even when biocides are included in the composition.

BACKGROUND OF THE INVENTION AND PRIOR ART

The utility of silanes, especially alkoxysilanes, as masonry waterrepellents is widely known. Compositions currently in use employsolutions of silanes in various organic solvents such as alcohol, e.g.,Seiler U.S. No. 3,772,065, and Brown et al. U.S. Pat. No. 4,342,796, orhydrocarbons, e.g., Linn, U.S. Pat. No. 4,525,213. Principal limitationsof such solvent type compositions include the toxicity and theflammability of the solvents employed.

Aqueous silane compositions which are non-toxic and non-flammable havebecome important as effective masonry water repellent compositions, see,Puhringer, U.S. Pat. No. 4,433,013, Schmidt, U.S. Pat. No. 4,517,375 andDePasquale and Wilson, U.S. Pat. No. 4,648,904. Such compositions canhave an important drawback, however, and that is that the pH may tend todrift and then the silane reacts with water and polymerizes. Thisreduces efficacy by reducing the content of active, water-repellentingredient. Moreover, the pH of the system may shift when additives areincluded such as a biocide, which is commonly added to retard growth offungi and the like. Although the stability of the water-containingemulsions can be enhanced to some extent by refrigerating them, or theproblem of reduced efficacy can be avoided by using the emulsions soonafter preparation, both expedients are not cost-effective and may insome cases cause waterproofing contractors to go back to theabove-mentioned solvent borne, non-aqueous compositions.

Although the prior art has frequently demonstrated that silanesdispersed in water react to form silicone resins, see, e.g., Hatcher etal., U.S. Pat. No. 2,683,674 and Raleigh, U.S. Pat. No. 4,175,159, noeasy way has been suggested to stabilize them. In some cases, the pH ofthe system has been adjusted to increase the rate of resin formation,e.g., Deubzer et al., U.S. Pat. No. 4,552,910 and Ona et al., U.S. Pat.No. 4,228,054, but pH control was not suggested as a stabilizing means.Stable hydrolyzed silane impregnating solutions useful as waterrepellents can also be prepared by dissolving some silanes in water asreported in the above-mentioned Puhringer and Schmidt patents, but theydeliberately hydrolyze the silanes and do not produce a stablehydrolyzed silane composition. Wilson, in commonly assigned U.S. PatentApplication, Ser. No. 189,146, filed May 2, 1989, now allowed, disclosesthat hydrolytically stable, water-based, normally hydrolyzable silaneemulsions may be prepared by selecting appropriate silanes (largelywater insoluble) and appropriate emulsifiers, if the pH is maintained ina predetermined pH stable range, typically 6-8, with a bufferingcompound. Additionally, Wilson, in commonly assigned U.S. PatentApplication, Ser. No. 317,714, filed Mar. 1, 1989, now allowed,discloses buffered silane emulsions compositions in combination withexpanded perlite.

However, modern environmental concerns of air quality have made itdesirable to develop water-repellents for porous substrates having lowlevels of volatile organic compounds when cured. Compounds of thisnature are especially desirable in light of the increasingly stringentstandards on volatile organics set forth by the Environmental ProtectionAgency (EPA). To this end, it has now been discovered that the bufferedsilane emulsions of the present invention are eminently suitable forboth providing stable compositions useful in rendering masonry, cementand expanded perlite surfaces water repellent, and possessing asufficiently low volatile organic compound content when cured to satisfyeven the most stringent air quality standards.

When used herein and in the appended claims the term "compound forbuffering the pH of said composition within said determinable pH stablerange" contemplates any substances or combination of substances, which,when dissolved in water produce a solution which resists a change in itshydrogen ion concentration upon the addition of acid or alkali. Althoughthis will call to the mind of those skilled in this art a large familyof buffering compounds, numerous illustrations of typical bufferingcompounds will be set forth hereinafter and in the working examples.

SUMMARY OF THE INVENTION

According to the present invention there are provided buffered aqueoussilane emulsions, useful as porous substrate water repellentcompositions and having a volatile organic compound content of less thanabout 400 g/l when cured, comprising effective amounts of: (a) ahydrolyzable silane essentially hydrolytically stable within adeterminable pH range; (b) at least one emulsifier having anhydrophile-lipophile balance (HLB) value of from about 1.5 to about 20,preferably 4 to 17; (c) an effective amount of at least one compound forbuffering the pH of said composition within said determinable pH stablerange; and (d) water.

In one of its embodiments, the present invention also provides a processfor increasing the resistance to penetration by aqueous media of aporous substrate by applying to the surface of the substrate a bufferedcomposition as above defined and allowing the composition to cure.

Special mention is made of embodiments of this invention comprisingcompositions and use of such compositions as defined above, wherein theyalso include an effective amount of (e) a biocide.

DETAILED DESCRIPTION OF THE INVENTION

By the term "masonry" used herein, is meant any porous inorganicsubstrate, particularly building compositions and including but notlimited to structural ceramics such as common brick, paving brick, facebrick, sewer pipe, drain tile, hollow block, terra cotta, conduits,roofing tile, flue lining, cements such as Portland cement, calcinedgypsum products, i.e., molding and building plaster and stucco, magnesiacement, insulation products such as electrical and thermal insulators(diatomaceous earth brick) and porcelain spark plugs, etc.

The masonry materials also include stone, tile, artificial stone, adobe,concrete and reinforced concrete such as found in roadways, bridgedecks, airport runways, parking garage decks, and other concretebuilding structures.

The masonry materials which can be treated in accordance herewith arepreferably dry when treated with the water repellent compositions,although they may be wet. In the case of settable masonry materials, thecompositions of the present invention may be incorporated in the presetmixture, for example, into a concrete mix prior to casting and setting.Wood, structural timbers, siding and the like can also be made waterrepellent using this invention.

By the term "expanded perlite", as used herein, is meant compositionswhich generally comprise any glass rock with the capacity to expandgreatly on heating and particularly comprises volcanic glass ofrhyolitic composition, containing 2 to 5 percent of combined water.Perlite is generally characterized by a system of concentric, spheroidalcracks which are called perlite structures. Expanded perlite denotes anyglass rock and more particularly a volcanic glass which has expandedsuddenly or "popped" while being heated rapidly. This "popping"generally occurs when the grains of crushed perlite are heated to thetemperatures of incipient fusion. The contained water is converted tosteam and the crushed particles form light, fluffy, cellular particles.Volume increases of the particles of at least ten fold are common.Different types of perlite are characterized by variations in thecomposition of the glass affecting properties such as softening point,type and degree of expansion, size of the bubbles and wall thicknessbetween them, and porosity of the product. See generally; EncyclopedicDictionary of Industrial Technology, Materials, Process and Equipment,(1984), pages 226-27 and Grant; Hackh' s Chemical Dictionary, TheBlakiston Company, Inc., 3rd Edition (1944).

The compositions of the present invention all possess a volatile organiccompound (VOC) content of less than about 400 g/l when cured, preferablyless than about 350 g/l, more preferably less than about 300 g/l andmost preferably less than about 250 g/l. The VOC content is determinedusing Environmental Protection Agency Method 24. The VOC content iscalculated according to the following equation: ##EQU1## where d=densityof material being tested according to ASTM D1475-85; S=percent solidsaccording to ASTM D2369-86; and W=percent water determined by ASTMD4017-81.

The Hydrolizable Silane (a). The water-based compositions of the presentinvention preferably include as component (a) a hydrolyzable silane, forexample, one with a molecular weight up to about 600 (or essentially amultiple thereof, if oligomerized) and the general formula of R_(n)--Si--(R¹)_(4-n), wherein R is a C₁ -C₃₀ hydrocarbyl or halogenatedhydrocarbyl group, R¹ is a C₁ -C₆ alkoxy, halide, amino, carboxyl, or amixture of any of the foregoing, and n is 1 or 2. The hydrocarbyl groupcomprises hydrogen and carbon atoms and may be aliphatic, orcycloaliphatic, or aryl, or aralkyl. These hydrocarbyl radicals may alsocontain as substituent groups, halogen, e.g., chlorine, bromine,fluorine; nitrogen; oxygen or sulfur heteroatoms. One or more of suchhalogen substituents may be present in the R group. Preferably the Rgroup is a C₆ -C₃₀ hydrocarbyl or halogenated hydrocarbyl and morepreferably the R group is C₈ -C₃₀ hydrocarbyl or halogenatedhydrocarbyl. The R¹ group can comprise a C₁ -C₆ alkoxy, halogen, amino,or carboxylate group. Thus, among the alkyl groups useful as R¹ aremethyl, ethyl, n-propyl, and isopropyl. As indicated, n may be 1 or 2and thus, monohydrocarbyl substituted alkoxysilanes and dihydrocarbylsubstituted alkoxysilanes are contemplated by the present invention. Theactive ingredients of the invention can also comprise condensationdimers and trimers, or other oligomers of the silanes, as are well knownin the art. The hydrolyzable silanes (a) can range widely in amount.However, typically the amount can comprise from about 1 to about 60percent by weight of the composition, and especially from about 10 toabout 50 percent by weight.

Silanes especially useful in accordance with the present inventiongenerally have a molecular weight in excess of 135 and preferablygreater than 190 up to about 600 for the monomers. The dimers andtrimers present in the composition will, of course, have essentiallymultiples of the molecular weights of the single specie of silane orsilanes being used. It should be noted that mixtures of various silanesmay be used, if desired.

Specific examples of silanes useful in accordance with the presentinvention include, but are not limited to, butyltrimethoxysilane,butyltriethoxysilane, dibutyldimethoxysilane, isobutyltrimethoxysilane,di-isobutyldimethoxysilane, isobutyltriethoxysilane,n-hexyltrimethoxysilane, 6-chloro-hexyltrimethoxysilane,6,6,6-trifluorohexyltrimethoxysilane, cyclohexyltrimethoxysilane,benzyltrimethoxysilane, 4-chlorobenzyltriethoxysilane,4-bromobenzyltri-n-propoxysilane, phenyltrimethoxysilane,phenyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane,octyltriisopropoxysilane, 2-ethylhexyltrimethoxysilane,4-chlorobenzyltrimethoxysilane, decyltrimethoxysilane,dodecyltrimethoxysilane, dodecyltribromosilane,tetradecyltriethoxysilane, hexadecyltriethoxysilane,octadecyltriethoxysilane, eicosyltrimethoxysilane,bis(octyldiethoxysiloxane)dimer, decyltriethoxysilane,dodecyltriethoxysilane, bis(dodecyldiethoxysiloxane) dimer,octadecyltrimethoxysilane, 1,3-diethoxyhexamethyltrisiloxane and thelike, mixtures of any of them and the like, alone, and in admixture withdimers, trimers and other oligomers thereof.

The Emulsifiers (b). A wide variety of ionic and nonionic emulsifiershave been tried and have been found to be useful in the presentinvention. Nonionic, anionic, cationic and amphoteric emulsifiers arewell known from the state of the art. The preferred emulsifiers are,however, nonionic. The concentration of emulsifier or emulsifiers (b)used in accordance with the present invention may range widely, butpreferably is from about 0.5 to about 50 percent by weight of the silane(a) and especially preferably in the range from about 1 to about 8percent by weight of the silane.

In general, those emulsifiers or emulsifier blends which have an HLB inthe range from about 1.5 to about 20, and preferably in the range fromabout 4 to about 17 may be used herein. The proper HLB value for a givensilane or silane mixture must be determined experimentally in order toascertain the optimum stability.

The HLB classification of surfactants is based on molecular structureand therefore can be used to predict the behavior of single molecules.HLB is determined experimentally by techniques known to those skilled inthis art, for example, those set forth in the pamphlet "The HLB System"published by ICI Americas, Inc., Wilmington, DE, U.S.A. See also thepublication "Adjuvants for Herbicides", Weed Society of America,Champaign, IL, U.S.A. If the HLB of an emulsifier is below 1.5, it willnot be useful in this invention because it will not produce a stableoil-in-water emulsion. If, on the other hand, the HLB is above 20, italso will not be useful because stability is poor. HLB values in therange of 4-17 are preferred because they provide the most stableemulsions of the above mentioned silanes.

Specific examples of emulsifying agents which may be used in accordanceherewith include, but are not limited to the following with the HLBvalue given in parenthesis following the name: sorbitan trioleate (1.8),sorbitan tristearate (2.1), polyoxyethylene sorbitol hexastearate (2.6),glycerol monostearate (3.8), sorbitan monooleate (4.3), sorbitanmonostearate (4.7), polyoxyethylene(2 mole) stearyl ether (4.9),sorbitan monopalmitate (6.7), polyoxypropylene mannitol dioleate (8),polyoxyethylene sorbitol oleate (9.2), polyoxyethylene stearate (9.6),polyoxyethylene sorbitan monooleate (10.0), polyoxyethylene monooleate(11.4), polyoxyethylene(6 mole) tridecyl ether (11.4),polyoxyethylene(10 mole) cetyl ether (12.9), polyoxyethylene sorbitanmonooleate (15), polyoxyethylene(20 mole) stearyl ether (15.3),polyoxyethylene(15 mole) tridecyl ether (15.4), polyoxyethylenealkylamine (cationic, 15.5); polyoxyethylene alcohols having an HLB of9.7, about 10, and 11.6; ethoxylated nonylphenols having HLB values of10, 11 and 12; dialkylphenol ethoxylates having an HLB value of 10.6;block copolymers of ethylene oxide and propylene oxide having HLB valuesin the range of 5.5 to 15; ethoxylated octyl phenols having an HLB ofabout 13.5, 17.3, and 17.9; fatty acid glycerides having an HLB value ofapproximately 4, sodium lauryl sulfate, sodium oleate, mixtures of anyof the foregoing, and the like.

The preferred emulsifying agents, given in the table below, provideespecially useful emulsions of silanes.

                  TABLE I                                                         ______________________________________                                        TYPE OF SURFACTANT                                                                            EXAMPLES (SUPPLIER; HLB)                                      ______________________________________                                        Polyoxyethylene alcohols                                                                      Brij 30 (ICI Americas; 9.7)                                                   Tertigol 15-S-3 (Union                                                        Carbide; approx. 10)                                                          Triton DF 16 (Rohm &                                                          Haas; 11.6)                                                   Ethoxylated nonyl phenols                                                                     NP-6 (Union Carbide; 11)                                                      NP-7-(Union Carbide; 12)                                                      CO-520 (GAF; 10)                                              Dialkyl phenol ethoxylate                                                                     DM-530 (GAF; 10.6)                                            Block copolymers of                                                                           Pluronics (BASF)                                              ethylene oxide and                                                                            L42 (8), L62 (7), L64 (15)                                    propylene oxide L72 (6.5), L92 (5.5),                                                         25R2 (6.3)                                                                    Tetronic 702 (BASF; 7)                                        Fatty acid glycerides                                                                         Arlacel 165 (ICI Americas; 4)                                 Sorbitan fatty acid esters                                                                    Spans (ICI Americas)                                                          20 (8.6), 40 (6.7), 60 (4.7)                                                  80 (4.3)                                                      Polyoxyethylene sorbitan                                                                      Tween 61 (ICI Americas; 9.6)                                  fatty acid esters                                                                             Tween 81 (ICI Americas; 10.0)                                                 Atlas G-1096                                                  Blends of sorbitan esters                                                                     Atlas G-2090 (ICI Americas)                                   with polyoxethylene amines                                                    Amphoteric      Atlas G-271 (ICI Americas)                                    Polyvinyl alcohol                                                                             (Air Products and                                                             Chemicals, Inc.)                                              Blend of octylphenol                                                                          Triton X-100 and                                              polyoxyethylene ethanol                                                                       Triton X-305 (Rohm &                                                          Haas, about 15)                                               ______________________________________                                    

Blending may be necessary, and desirable, if one of the emulsifiers,e.g., sodium lauryl sulfate, has an HLB ouside the range of 1.5-20.Sodium lauryl sulfate, HLB about 40, will be blended with a low HLBmaterial, as illustrated above, for use.

Buffering agents. Agents for buffering the compositions within the pHrange optimum for silane stability can vary widely in type and amount.The selection of a suitable buffering agent is readily made bytechniques well known to those of ordinary skill in this art. Especiallyconvenient is to prepare a silane composition comprising the silane (a),the emulsifier (b), and water (c) in accordance with the teachings ofDePasquale and Wilson, U.S. Pat. No. 4,648,904, and to measure the pHand silane concentration initially and then to add the buffering agentcandidate. The candidate to be acceptable should maintain the pH levelwithin the said determinable pH range, even when adding substantialquantities of acid or bases, which would ordinarily cause the pH toswing into areas in which substantial silane hydrolysis will occur.Swings of plus or minus one pH unit are tolerable. Also relevant wouldbe a pH swing induced by additions of a biocide that materially alterspH and promotes hydrolysis. Two methods are convenient for measuringlong term stability: one is to determine final pH and final silanecontent, after aging, and the other is to performance test the silaneemulsions on mortar cubes using standard test methods, such as thosedescribed in the above-mentioned DePasquale and Wilson patent. In theformer, using an unsuitable buffering compound will not prevent the pHfrom swinging into a range promoting hydrolysis, e.g., from 7.5 to 4.0and the final silane concentration will be materially reduced, e.g., cutfrom 40 percent to 20 percent and, in extreme cases, all the way down tozero percent. Such a test should be carried out over a significant timeperiod, e.g., after aging the emulsion under test for up to 12 months atroom temperature. In the performance test, a 2 inch mortar cube iscoated in duplicate with the test emulsion and the coating cured, thenimmersed in water for 21 days. The percent reduction in weight gain ofcompound treated cubes compared to untreated control cubes is indicativeof the retention of silane content and the efficacy of the bufferingagent.

In initial experiments, emulsions were unbuffered and prepared inaccordance with prior art procedures. They contained biocide whichdecomposed to acetic acid and lowered the pH to 4. Within a month ofmanufacture, such emulsions showed decreased performance in the waterrepellency test set forth above. They also showed reduced silaneconcentration, as determined by gas chromatography. After 5 months thestate of the art emulsion performed very poorly in water repellencytests on concrete.

Numerous experiments which followed demonstrated that various bufferswere effective in raising the pH of the state of the art emulsion toabout 7.5, and maintaining the effectiveness of the formulation over aperiod of time.

When emulsions of predominantly n-octyltriethoxysilane, PCR, Inc.'sPROSIL® 9202 organofunctional silane, buffered in this manner, wereanalyzed by gas chromatography after one year, over 95 percent of thesilane remained unhydrolyzed. Moreover, unbuffered emulsions at pH 4showed less than 5 percent unhydrolyzed silane after a similar period,indicating the long term stabilizing effect of the buffering compound.

Although buffers are especially important when the emulsion components,particularly biocides, shift the pH away from neutrality, experimentshave shown that in other emulsions which are inherently neutral, pH 7,without use of a buffer, the silane remains substantially unhydrolyzedfor many months. In such cases the emulsions do not contain a biocide,or they contain an alternative biocide, that does not alter theinherently neutral pH.

Illustrative of buffering agents useful for silane emulsions, especiallythose containing biocides are: organic and inorganic acids and bases,including salts thereof, and preferably mono- or poly-alkali metal,alkaline earth metal or amine salts of carbonic acid, phosphoric acid,sulfuric acid, hydrosulfuric acid, a C₁ -C₆ organo-, mono- orpoly-carboxylic acid, or a C₂ -C₃₀ alkyleneiminopolycarboxylic acid,ammonia, a C₁ -C₃₀ organic base, or a mixture of any of the foregoing.Illustrative are: sodium bicarbonate, sodium carbonate, ammoniumcarbonate, sodium borate, mono-, di-, or trisodium phosphate, mono-,di-, or tripotassium phosphate, ammonium sodium phosphate, mono-, ordisodium sulfate, sodium acetate, potassium acetate, ammonium acetate,calcium acetate, sodium formate, mono-, or disodium sulfide, ammonia,mono-, di, or triethylamine, mono-, di-, or triethanolamine,(ethylenedinitrilo) tetraacetic acid sodium salt (sodium E.D.T.A.),pyridine, aniline, and sodium silicate. These are only a few examples ofappropriate buffering agents. Combinations of these materials with otherbuffers, acids, or bases, such as the use of ammonium hydroxide andacetic acid together, will also be effective.

Trisodium phosphate (Na₃ PO₄) and ammonium hydroxide (NH₄ OH) arepreferred, but sodium bicarbonate (NaHCO₃) is especially preferredbecause it is easy to handle; it consistently gives emulsions with a pHof 7.5; it is environmentally safe; and it is inexpensive.

The amount of buffering agent to be employed can vary widely. Ingeneral, however, less than 0.01 percent will not be enough to beuseful, and more than 5 percent by weight of the total composition willbe uneconomical.

If a biocidal agent (e) is used, any of those well known in the art forimparting antimicrobial and biocidal activity can be used inconventional amounts, e.g., from about 0.1 to about 5 percent by weightbased on the composition. Suitable biocidal agents for these embodimentscomprise 6-acetoxy-2,4-dimethyl-m-dioxane, sold by Givaudan Corp. underthe trademark Giv-Gard DXN biocide, methyl p-methoxy benzoate, and thelike. Typical concentrations of these biocides are 0.15 percent byweight.

In addition to biocides, the buffer stabilized formulations of thisinvention may include other additives such as fragrances, colorants,thickeners, foaming agents, anti-foaming agents, and the like.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate the present invention but the claimsare not to be construed as limited thereto.

EXAMPLE 1

To a mixture of 200 g of octyltriethoxysilane and 8 g of an emulsifiermixture comprising 70 percent of octylphenol polyethyleneoxyethanol(Rohm & Haas Triton® X-100) and 30 percent of octylphenolpolyethyleneoxyethanol (Rohm & Haas Triton® X-305) HLB of about 15, in aWaring Blendor® mixer is slowly added 292 g of deionized water whichcontains 6-acetoxy-2, 4-dimethyl-m-dioxane biocide (Givaudan Corp.GIV-GARD® DXN biocide) in an amount to provide 0.15 percent ultimateconcentration; and 0.10 percent sodium bicarbonate as a buffering agent.Mixer speed is gradually increased to provide good dispersion withoutincorporating a large amount of air. After complete addition, themixture is stirred at high speed for an additional five minutes toprovide a buffered emulsion in accordance with this invention, having apH of 7.5, and which maintains its homogeneous, milky appearance for upto a year or more at room temperature (Example 1). For comparisonpurposes, an emulsion is prepared in exactly the same way but the sodiumbicarbonate buffer is omitted. The pH of this emulsion is 4.0(Comparative Example 1A). For purposes of further comparison, anemulsion is prepared in the same way, but the biocide is replaced with0.15 percent of methyl p-methoxy benzoate and the sodium bicarbonatebuffer is omitted. The pH of this emulsion is 7.0. (Comparative Example1B).

The emulsions of Example 1 and Comparative Examples 1A and 1B areanalyzed initially for the concentration of silane, H₁₇ C₈ Si(OC₂ H₅)₃,and dimer, H₁₇, C₈ Si(OC₂ H₅)₂ -O-Si(OC₃ H₅)₂ C₈ H₁₇ by gaschromatography using a 1/8 in. ×10 ft. 20 percent SP-2100 column,temperature programmed from 100° to 280° C. at 16° C./min., usingoctamethylcyclotetrasiloxane as an internal standard. After 12 months ofaging at about 23° C., the emulsions are again examined for pH andsilane concentration. The results obtained are set forth in Table 1:

                  TABLE 1                                                         ______________________________________                                        Silane Concentration and pH of Emulsions                                      Before and After aging at 23° C. for 1 year.                           EXAMPLE      1            1A     1B                                           ______________________________________                                        Initial pH   7.5          4.0    7.0                                          Initial silane                                                                             40           40     40                                           Concentration, %                                                              Final pH     7.5          4.0    5.5                                          Final Silane 40           0      20                                           Concentration, %                                                              ______________________________________                                    

The foregoing data show that a buffering agent in accordance with thisinvention maintains substantially all of the silane in an unhydrolyzedcondition, whereas without the buffering agent the silane content is cutin half or even completely eliminated during long term storage.

For performance testing, aged emulsions prepared as described in Example1 and Comparative Example 1A above are tested using concrete cubes inaccordance with DePasquale and Wilson, U.S. Pat. No. 4,648,904. Cementmortar cubes two inches on the side are conditioned in a control room at73° F. and 50 percent relative humidity for 21 days to give a constantweight. Each composition to be tested for water repellency is applied totwo cubes at the rate of 125 square feet per gallon (3.07 square metersper liter), and the coated cubes are cured on a rack in a control roomfor 13 days prior to recording the initial weight of each cube. All ofthe cubes including two untreated control cubes are placed on a rack andimmersed in a distilled water bath. After 21 days of immersion the cubesare removed, blotted dry and immediately weighed. The percent weightgain of each block is determined by ##EQU2##

The percent Reduction of Weight Gain is calculated by the formula##EQU3## Higher Reduction of Weight Gain indicates higher effectivenessas a porous material water repellent. Due to the variability of themortar blocks, values for % Reduction of Weight Gain have a precision ofabout plus or minus 5 percent.

The results of concrete water absorption of the aged emulsions are setforth in Table 2:

                  TABLE 2                                                         ______________________________________                                        Concrete Water Absorption using buffered                                      Silane Eulsions                                                                           REDUCTION OF WEIGHT GAIN %                                        Age of Emulsion                                                                           EXAMPLE                                                           months      1             1A                                                  ______________________________________                                         0.25       74            --                                                  0.5         --            68                                                  1.0         74            --                                                  2.0         --            52                                                  3.0         74            --                                                  5.0         --            46                                                  7.0         71            --                                                  9.0         71            --                                                  12.0        68             5                                                  ______________________________________                                    

The beneficial effect of using a buffering agent as suggested by silanecontent data in Table 1 is confirmed by actual water absorption testsset forth in Table 2.

EXAMPLE 2

The procedure of Example 1 is repeated, substituting for the emulsifierused, 3 percent by weight of sorbitan fatty acid esters known as Span®20 and Span® 60 and polyoxyethylene sorbitan fatty acid esters known asTween® 81. Spans and Tweens are trademarks of ICI Americas Corp. Stablebuffered emulsions in accordance with this invention are obtained.

EXAMPLES 3 AND 4

The procedure of Example 1 is repeated, substituting for the sodiumbicarbonate, disodium hydrogen phosphate and a mixture of ammoniumhydroxide and acetic acid as buffering agents. Storage stable aqueousemulsions in accordance with this invention are obtained.

EXAMPLES 5-17

The procedure of Example 1 is followed to produce a variety of bufferedaqueous silane emulsions. Table 3 below summarizes the theoretical VOCfor these buffered aqueous silane emulsions.

                                      TABLE 3                                     __________________________________________________________________________    THEORETICAL VOC'S FROM SILANES/SILOXANES                                                                          Theoretical                                                                           Density                                                                            Theoretical.sup.b            Example                                                                            Silane/Siloxane                                                                            Formula                                                                              MW  Solids MW.sup.a                                                                      Percent Solids.sup.a                                                                  (g/ml)                                                                             VOC(g/l)                     __________________________________________________________________________     5   Isobutyltrimethoxysilane                                                                   C.sub.7 H.sub.18 O.sub.3 Si                                                          178.30                                                                            109.20 61.2    0.933                                                                              360                           6   Octyltriethoxysilane                                                                       C.sub.14 H.sub.32 O.sub.3 Si                                                         276.49                                                                            165.31 59.8    0.88 350                           7   Bis(octyldiethoxysiloxane)                                                                 C.sub.24 H.sub.54 O.sub.5 Si.sub.2                                                   478.86                                                                            330.61 69.0    0.91 280                               dimer                                                                     8   Octyltrimethoxysilane                                                                      C.sub.11 H.sub.26 O.sub.3 Si                                                         234.41                                                                            165.31 70.5    --   --                            9   Decyltriethoxysilane                                                                       C.sub.16 H.sub.36 O.sub.3 Si                                                         304.55                                                                            193.37 63.5    --   --                           10   Decyltrimethoxysilane                                                                      C.sub.13 H.sub.30 O.sub.3 Si                                                         262.47                                                                            193.37 73.7    0.907                                                                              240                          11   Dodecyltriethoxysilane                                                                     C.sub.18 H.sub.40 O.sub.3 Si                                                         332.60                                                                            221.42 66.6    0.88 290                          12   Bis(dodecyldiethoxy-                                                                       C.sub.32 H.sub.70 O.sub.5 Si.sub.2                                                   591.08                                                                            442.84 74.9    0.893                                                                              220                               siloxane)dimer                                                           13   Tetradecyltriethoxysilane                                                                  C.sub.20 H.sub.44 O.sub.3 Si                                                         360.66                                                                            249.41 69.2    --   --                           14   Hexadecyltriethoxysilane                                                                   C.sub.22 H.sub.48 O.sub.3 Si                                                         388.71                                                                            277.53 71.4    0.859                                                                              250                          15   Octadecyltriethoxysilane                                                                   C.sub.24 H.sub.52 O.sub.3 Si                                                         416.76                                                                            305.58 73.3    0.87 230                          16   Octadecyltrimethoxysilane                                                                  C.sub.21 H.sub.46 O.sub.3 Si                                                         374.68                                                                            305.58 81.6    --   --                           17   1,3-Diethoxyhexamethyl-                                                                    C.sub.10 H.sub.28 O.sub.4 Si.sub.3                                                   296.59                                                                            222.47 75.0    0.890                                                                              220                               trisiloxane                                                              __________________________________________________________________________     MW = molecular weight                                                         .sup.a Theoretical percent solids are based on total hydrolysis and           condensation of the silane/siloxane RSi(OR).sub.3 → RSiO.sub.3/2       .sup.b Theoretical VOC is calculated according to the formula VOC (g/l) =     d(100010S) wherein VOC is volatile organic compounds, d is the density of     the silane/siloxane in g/ml, and S is the theoretical percent solids.    

Thus, Table 3 above demonstrates that the compositions of the presentinvention possess volatile organic compound contents of less than 400g/l when cured and some exhibit content levels of less than 250 g/l,making them eminently suitable for use as water proofing sealants evenunder the strictest environmental air quality regulations.

The above-mentioned patents, patent applications, publications and testmethods are incorporated herein by reference.

Many variations of the invention will suggest themselves to thoseskilled in this art in light of the above, detailed description. Forexample, the silane can comprise isobutyltrimethoxysilane,octadecyltriethoxysilane, 4R-triethoxysilylmenthene-1, mixtures thereof,and the like. Instead of 40 percent by weight, the composition cancomprise 20 percent by weight of silane. The biocide can be omitted. Themasonry surface can be an expanded perlite or any cement composition.All such obvious variations are within the full intended scope of theappended claims.

We claim:
 1. A buffered aqueous silane emulsion composition having avolatile organic compound content of less than about 400 g/l aftercuring comprising effective amounts of:(a) a hydrolyzable silaneessentially hydrolytically stable within a determinable pH range; (b) anemulsifier or mixture of emulsifiers having an HLB value of from about1.5 to about 20; (c) at least one compound for buffering the pH of saidcomposition within said determinable pH stable range; and (d) water. 2.A composition as defined in claim 1 wherein said composition has avolatile organic compound content of less than about 350 g/l.
 3. Acomposition as defined in claim 2 wherein said composition has avolatile organic compound content of less than about 300 g/l.
 4. Acomposition as defined in claim 3 wherein said composition has avolatile organic compound content of less than about 250 g/l.
 5. Acomposition as defined in claim 1 wherein said hydrolyzable silane (a)comprises from about 1 to about 60 percent by weight of the composition;said emulsifier (b) comprises from about 0.5 to about 50 percent byweight based on (a); said compound for buffering (c) comprises fromabout 0.01 to about 5 percent by weight based on (a), (b), (c) and (d)combined; and water (d) is present in an amount sufficient to provide100 percent by weight.
 6. A composition as defined in claim 1 whereinsaid hydrolyzable silane has a molecular weight of up to about 600 andcomprises a compound of the general formula

    R.sub.n --Si--(R.sup.1).sub.4-n

wherein R is C₁ -C₃₀ hydrocarbyl or halogenated hydrocarbyl, R¹ is C₁-C₆ alkoxy, halide, amino carboxyl or a mixture of any of the foregoingand n is 1 or 2, or an oligomer of said compound.
 7. A composition asdefined in claim 6 wherein R is C₆ -C₃₀ hydrocarbyl or halogenatedhydrocarbyl.
 8. A composition as defined in claim 7 wherein R is C₈ -C₃₀hydrocarbyl or halogenated hydrocarbyl.
 9. A composition as defined inclaim 6 wherein said silane comprises an alkylalkoxysilane.
 10. Acomposition as defined in claim 9 wherein said silane comprises analkyltrialkoxysilane.
 11. A composition as defined in claim 6 wherein Rcomprises a C₄ -C₁₂ alkyl group, R¹ comprises a C₁ -C₃ alkoxy group andn is
 1. 12. A composition as defined in claim 6 wherein R comprises a C₆-C₁₂ alkyl group.
 13. A composition as defined in claim 1 wherein saidsilane comprises octyltriethoxysilane.
 14. A composition as defined inclaim 1 wherein said silane comprises isobutyltrimethoxysilane.
 15. Acomposition as defined in claim 1 wherein said silane comprisesbis(octyldiethoxysilane) dimer.
 16. A composition as defined in claim 1wherein said silane comprises octyltrimethoxysilane.
 17. A compositionas defined in claim 1 wherein said silane comprisesdecyltriethoxysilane.
 18. A composition as defined in claim 1 whereinsaid silane comprises dodecyltriethoxysilane.
 19. A composition asdefined in claim 1 wherein said silane comprisesbis(dodecyldiethoxysiloxane)dimer.
 20. A composition as defined in claim1 wherein said silane comprises tetradecyltriethoxysilane.
 21. Acomposition as defined in claim 1 wherein said silane compriseshexadecyltriethoxysilane.
 22. A composition as defined in claim 1wherein said silane comprises octadecyltriethoxysilane.
 23. Acomposition as defined in claim 1 wherein said silane comprisesoctadecyltrimethoxysilane.
 24. A composition as defined in claim 1wherein said silane comprises 1,3-diethoxyhexamethyltrisiloxane.
 25. Acomposition as defined in claim 5 wherein the concentration of saidsilane (a) comprises from about 10 to about 50 percent by weight of saidcomposition.
 26. A composition as defined in claim 1 wherein saidemulsifier (b) has an HLB value of from about 4 to about
 17. 27. Acomposition as defined in claim 1 wherein said emulsifier (b) comprisesat least one nonionic emulsifying agent.
 28. A composition as defined inclaim 27 wherein said emulsifier (b) comprises at least one alkylphenolpolyethyleneoxyethanol.
 29. A composition as defined in claim 28 whereinsaid emulsifier (b) comprises at least one octylphenolpolyethyleneoxyethanol.
 30. A composition as defined in claim 5 whereinthe concentration of said emulsifier (b) comprises from about 1 to about8 percent by weight based on silane (a).
 31. A composition as defined inclaim 1 wherein said compound for buffering (c) comprises a mono- orpoly-alkali metal, alkaline earth metal or amine salt of carbonic acid,phosphoric acid, sulfuric acid, hydrosulfuric acid, a C₁ -C₆ organo-,mono- or poly-carboxylic acid, or a C₂ -C₃₀ alkyleneiminopoly carboxylicacid, ammonia, a C₁ -C₃₀ organic base, or a mixture of any of theforegoing.
 32. A composition as defined in claim 31 wherein saidcompound for buffering (c) comprises an alkali metal carbonate or-bicarbonate, or -phosphate or ammonia.
 33. A composition as defined inclaim 32 wherein said compound for buffering (c) comprises sodiumbicarbonate.
 34. A composition as defined in claim 1 wherein the saidbuffering compound (c) provides a pH in the range of from about 6 toabout
 8. 35. A composition as defined in claim 34 wherein said bufferingcompound (c) provides a pH of about 7.5.
 36. A composition as defined inclaim 1 which also includes(e) a small, effective amount of a biocide.37. A process for increasing the resistance to penetration by aqueousmedia of a porous substrate, said process comprising:(i) applying to thesurface of said substrate a buffered aqueous silane emulsion compositionhaving a volatile organic compound content of less than about 400 g/lwhen cured comprising effective amounts of:(a) a hydrolyzable silaneessentially hydrolytically stable within a determinable pH range; (b) anemulsifier or mixture of emulsifiers having an HLB value of from about1.5 to about 20; (c) at least one compound for buffering the pH of saidcomposition within said determinable pH stable range; and (d) water; and(ii) allowing said composition to cure.
 38. A process as defined inclaim 37 wherein said composition has a volatile organic compoundcontent of less than about 350 g/l.
 39. A process as defined in claim 38wherein said composition has a volatile organic compound content of lessthan about 300 g/l.
 40. A process as defined in claim 39 wherein saidcomposition has a volatile organic compound content of less than about250 g/l.
 41. A process as defined in claim 39 wherein said poroussubstrate comprises masonry, cement, expanded perlite or wood.
 42. Aprocess as defined in claim 37 wherein said hydrolyzable silane (a)comprises from about 1 to about 60 percent by weight; said emulsifier(b) comprises from about 0.5 to about 50 percent by weight based on (a);said compound for buffering (c) comprises from about 0.01 to about 5percent by weight based on (a), (b), (c) and (d) combined; and water (d)in an amount sufficient to provide 100 percent by weight.
 43. A processas defined in claim 37 wherein said hydrolyzable silane has a molecularweight of up to about 600 and comprises a compound of the generalformula

    R.sub.n --Si--(R.sup.1).sub.4-n

wherein R is C₁ -C₃₀ hydrocarbyl or halogenated hydrocarbyl group, R¹ isC₁ -C₆ alkoxy, halide, amino carboxyl or a mixture of any of theforegoing and n is 1 or 2, or an oligomer of said compound.
 44. Aprocess as defined in claim 43 wherein R is a C₆ -C₃₀ hydrocarbyl orhalogenated hydrocarbyl.
 45. A process as defined in claim 44 wherein Ris C₈ -C₃₀ hydrocarbyl or halogenated hydrocarbyl.
 46. A process asdefined in claim 43 wherein said hydrolyzable silane comprises analkylalkoxysilane.
 47. A process as defined in claim 43 wherein saidhydrolyzable silane comprises an alkyltrialkoxysilane.
 48. A process asdefined in claim 43 wherein said hydrolyzable silane comprises a C₄ -C₁₂alkyl group, R¹ comprises a C₁ -C₃ alkoxy group and n is
 1. 49. Aprocess as defined in claim 43 wherein said hydrolyzable silanecomprises a C₆ -C₁₂ alkyl group.
 50. A process as defined in claim 43wherein said hydrolyzable silane comprises octyltriethoxysilane.
 51. Aprocess as defined in claim 37 wherein said silane comprisesisobutyltrimethoxysilane.
 52. A process as defined in claim 37 whereinsaid silane comprises bis(octyldiethoxysiloxane)dimer.
 53. A process asdefined in claim 37 wherein said silane comprises octyltrimethoxysilane.54. A process as defined in claim 37 wherein said silane comprisesdecyltriethoxysilane.
 55. A process as defined in claim 37 wherein saidsilane comprises dodecyltriethoxysilane.
 56. A process as defined inclaim 37 wherein said silane comprisesbis(dodecyldiethoxysiloxane)dimer.
 57. A process as defined in claim 37wherein said silane comprises tetradecyltriethoxysilane.
 58. A processas defined in claim 37 wherein said silane compriseshexadecyltriethoxysilane.
 59. A process as defined in claim 37 whereinsaid silane comprises octadecyltriethoxysilane.
 60. A process as definedin claim 37 wherein said silane comprises octadecyltrimethoxysilane. 61.A process as defined in claim 37 wherein said silane comprises1,3-diethoxyhexamethyltrisiloxane.
 62. A process as defined in claim 37wherein the concentration of said hydrolyzable silane comprises fromabout 10 to about 50 percent by weight of said composition.
 63. Aprocess as defined in claim 37 wherein said emulsifier (b) has an HLBvalue of from about 4 to about
 17. 64. A process as defined in claim 37wherein said emulsifier (b) comprises at least one nonionic emulsifyingagent.
 65. A process as defined in claim 37 wherein said emulsifier (b)comprises at least one alkylphenol polyethyleneoxyethanol.
 66. A processas defined in claim 37 wherein said emulsifier (b) comprises at leastone octylphenol polyethyleneoxyethanol.
 67. A process as defined inclaim 37 wherein said emulsifier (b) comprises from about 1 to about 8percent by weight based on silane (a).
 68. A process as defined in claim37 wherein said compound for buffering comprises a mono- or poly-alkalimetal, alkaline earth metal or amine salt of carbonic acid, phosphoricacid, sulfuric acid, hydrosulfuric acid, a C₁ -C₆ organo-, mono-, orpolycarboxylic acid, or a C₂ -C₃₀ alkyleneiminopolycarboxylic acid,ammonia, a C₁ -C₃₀ organic base, or a mixture of any of the foregoing.69. A process as defined in claim 37 wherein said compound for buffering(c) comprises an alkali metal carbonate or -bicarbonate, or -phosphate,or ammonia.
 70. A process as defined in claim 37 wherein said compoundfor buffering (c) comprises sodium bicarbonate.
 71. A process as definedin claim 37 wherein said compound for buffering (c) provides a pH in therange of from about 6 to about
 8. 72. A process as defined in claim 37wherein said compound for buffering (c) provides a pH of about 7.5. 73.A process as defined in claim 37 wherein said composition includes.(e) asmall, effective amount of a biocide.
 74. A process as defined in claim37 wherein curing step (ii) is carried out at a temperature of fromabout 5° to about 50° C. for from about 4 hours to about 350 hours.